Hello. It is @hunhani.

Thank you for your interest and support in the previous posts. I will do my best to meet your expectations.

Last time, We have learned about the basic principles of quantum computers compared to ordinary computers.

Chapter 2. Magical phenomena of nature, quantum superposition & entanglement This time, let's deal with the magical phenomena of nature that are caused by quantum superposition and quantum entanglement, especially the measurement of quantum states and quantum transitions.

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Simple Review

Quantum computer uses a state in which all possible states overlap and are entangled

• Natural phenomena are determined by probability.
• Measurement or perturbation behavior itself affects the state.

Term Definition

• Quantum superposition : Quantum mechanical properties that exist simultaneously in all possible states that a particle can have in relation to energy or position.
• Qquantum entanglement : A state in which two or more quantum states are closely associated with one another. In the entangled state, states are inevitably determined depending on the fact that the other states are determined even in the separated physical system.

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As a result of the measurement, the initial quantum state can not be known!

When two or more particles are closely related to each other, they cause entanglement by overlapping (superposition) states. The individual states of the two particles entangled in a quantum entanglement are never known until they are measured. This is because it affects the instantaneous state of the measurement and confirms it as one of the specific inherent states allowed. Acquiring information about a system through measurement inevitably disturbs the state of the system.

To help you understand, let's compare this to a situation in reality.

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Measurement in the classic state

“A” measures 1kg of mass and 1cm of square steel plate.

Repetition of several measurements does not change the mass and length of the steel plate under the same physical conditions (isothermal, isobaric). Measuring the mass does not change the length, and measuring the length will not change the mass. The measurement in the classical state can not be said that the measurement action affects the state. Also, the initial state can be fully estimated by the measurement result.

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Measurement in the quantum state

A and B are lovers.

Case (1)
A: B, I love you.
B: I really love you too!
→ B feels a greater love to A who expresses love.

Case (2)
A: B, I love you.
B: Oh, yes. Thanks~
→ B did not express his or her intention, but B feel burdened inside and concern that he or she really love A.

In case (1), “A” and “B” will love more each other. But in the case (2), “A” may express the love in a bad way, and it may be that “B” has exacerbated the relationship between the two. When “A” express love, “A” can guess the answer and reaction of “B” based on the relationship between “A” and “B”, but no one knows what kind of result really happens. Likewise, measurement of the quantum state affects the state of the measurement action and can not sufficiently predict the initial state of the measurement.

It may be a rather sloppy analogy, but did you get a little more understanding?

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Quantum entanglement transcends the principle of locality!

If we determine the state of one of the two quantum entangled quantities through the measurement, we can immediately determine the state of the other. It is as if the information is moving instantaneously from one system to another system in an instant. This phenomenon is called quantum teleportation.

The principle of physics locality says that two objects that are spaced far apart can never directly affect each other. In order to influence each other, it is necessary to exchange information in anyhow and information about the state of the system in the transmission of information can be always mediated only through the surrounding of system.

For example, let's think of the earth orbiting around the sun, assuming that there exists only sun and the earth in the universe. If the sun suddenly disappeared from the universe at any moment, what would happen to the earth's movement? Classically, as soon as the sun disappears, the earth can be thought of as moving straight out of its orbit. However, considering the theory of relativity, applying the principle of locality, the linear motion of the earth begins after the sun has disappeared and its influence has propagated at the speed of light to reach the earth.

Three physicists (Albert Einstein, Boris Podolsky, Nathan Rosen) directly refuted the Copenhagen interpretation with the EPR theory that physical presence must have such a locality.

Ultimately, through John Stuart Bell's experiments, it revealed that quantum entanglement can not be applied to the principle of locality and that information can be mediated without going around the system. The EPR theory is not a truth that can be applied to all physics and is not explained in the quantum entanglement state. So it remains the name of the EPR paradox and is often mentioned in connection with the reversal of causality and the destruction of synchronicity.

Einstein said “God did not play backgammon.” He have established the theory of relativity, which can be called the beginning of quantum mechanics. However, he have shown the most negative attitude to quantum mechanics by axioms that natural phenomena are subject to probability. Is it surprising that Einstein even said something wrong?

The quantum entanglement state free from the principle of locality shows that the state of one particle can instantly determine the state of another particle.

Technically, transferring quantum information between two entangled atoms has been successful, but it has not yet been realized at the molecular level. However, this does not mean that information is transmitted faster than light, contrary to the axiom of relativity. In addition, quantum teleportation is transferring information from one location to another without having to move real physical particles. Therefore, we should not overlook that quantum teleportation is only relevant for the transfer of information for the communication means * not the transportation* means. Recalling the scene on the movie star track, some people think of quantum teleportation as a kind of cut-and-paste delivery concept in which the object is resolved into particles and moved another place then reassembled again. Please correct misunderstandings in this time.

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Next time, we will deal with how quantum parallelism due to quantum superposition and quantum entanglement relates to quantum communication security.

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I want to deliver it as easily as possible, but this topic is very difficult for everyone. If you comment your question, I will reply to you as easily and concisely as I can.

The following chapter is introduced.

Chapter 3. Janus-faced quantum computer? Quantum Parallelism & Quantum Communication Security

Please do not take your eyes off!

Previous Story

• [Quantum Computer & Blockchain Security] Chapter 0. Introduction
• [Quantum Computer & Blockchain Security] Chapter 1. Quantum computer! What the hell is different with ordinary computer?
• [Review] 18 Stories to See “Interstellar” Movie More Fun with Physics
• Engineer Dream Diodes with a Graphene Interlayer

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• All images used in this post are from Google Images.

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# YHH

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